Highly water absorbing foams have been used for cleaning a surface and for maintaining and removing water contents in a variety of fields including applications where water contents should be avoided or kept, for example, as wipers for wiping off water from any surface in clean rooms where semiconductors, hard discs, and liquid crystal display glass plates are produced, swabs for cleaning building glazing, articles for water wiping after car wash, for sweat absorption and thermal insulation, and for aqueous cultivation as well as wipers, ink absorbers, water-absorbing rolls, and household goods.
In the prior art manufacture of business machines, Freon was used to clean hard discs. Since the recognition of the fact that Freon is deleterious to the global environment by breaking the ozone layer, Freon washing has been replaced by water washing. It is then necessary to completely remove water after washing. There is a need for a material which is useful for water removal.
Most water absorbing foams used in such applications are PVA foams based on polyvinyl alcohol. Special polyurethane foams obtained by modifying flexible polyurethane foam which is originally hydrophobic so that it may become water absorbing are used in some applications as disclosed in U.S. Pat. Nos. 5,460,655 and 5,415,627.
The currently used PVA foams have a sufficient water absorbing capacity, but when dried, convert into a non-elastic solid state, which can damage or deform objective surfaces upon reuse. Additionally, the PVA foams are expensive.
While polyurethane foams are prepared using a polyol as one of main raw materials, it was proposed to increase the water absorbing capacity of polyurethane foam by using a special polyol containing much ethylene oxide. The resulting foam remains flexible and elastic even in a dry state, and its water absorbing capacity is improved to some extent, but not comparable to that of PVA foams. Since a special polyol is used, the foam is naturally expensive.